Everything can still happen to them and the worst possibility such as injury must be anticipated from the start because it is clear that currently there are several clubs who have experienced the severity of the injury storm which has made it difficult for their clubs such as Chelsea in wading into the EPL and of course Barcelona who must return to Europe. League due to injuries to their players.
Currently Arsenal are in very good condition so they have to anticipate all bad possibilities for them to continue to be consistent in the EPL and Europa League.
I believe Arsenal are one of the favorites in the Europa League this season. Their game is very good and I watch their game more often every chance I get, it's very entertaining. But you're right, player injuries are the most likely worry that every team thinks about right now given the very busy schedule.
But for now the round of 16 matches are still very far from Arsenal. They still have time to stay focused on the Premier League while waiting for who will be drawn for the next opponent. So it's still safe to say Arsenal are the favorites if they're only going to meet weak teams in the last 16.
Currently, through Arteta's statement, it seems that Arsenal will continue to look for players, especially those participating in the world cup this time, to continue to make them stronger. and indeed this is a good thing, especially since we also know that they have to do something like this in order to continue to strengthen them on every front.
On the other hand, I quite agree with what you said about hoping they find a team that can be said to be easy to face in the draw later, especially if you look at the current condition of the Europa League, it is quite scary because it is filled with several big clubs.